Danielle Macdonald, 25, was met with a thunderous standing ovation Monday when she walked onstage after the world premiere of coming-of-age dramedy Patti Cake$, in which the Australian actress plays a blue-collar New Jersey teen with hip-hop aspirations. The scrappy underdog story has already been scooped up by Fox Searchlight for $9.5 million after a fierce bidding war, thanks in no small part to Macdonald's magnetism in the titular role.

Nicknamed "Patti Cakes" by her ailing grandmother (Cathy Moriarty) and "Killa P" by her supportive pal (Siddharth Dhananjay), Patricia (Macdonald) dreams of becoming a rap megastar, but sheepishly confines her crude bars to the pages of her journal. It doesn't help that her domineering, alcoholic mother (Bridget Everett) mocks her musical ambitions at every turn, forcing Patti to pick up bartending and catering gigs to make ends meet.

But things start looking up when Patti meets enigmatic musician Basterd, the Antichrist (Mamoudou Athie), who lays down unusual beats for her to spit over and joins her hip-hop collective PBNJ. The supergroup releases a mixtape and plays a disastrous first gig at a strip club, but eventually finds its voice at a talent show for industry honchos.

Casting the character of Patti, "I really wanted an actress," first-time writer/director Geremy Jasper said during an audience Q&A. "I didn't want to do an 8 Mile thing where I got a rapper and then tried to turn them into an actress." When producers handed him a picture of Macdonald, "I just said, 'That's the girl. That's the image I had in my brain.' "

Macdonald, who recently appeared in American Horror Story: Roanoke, had no prior musical experience and trained for two years to learn how to rap. Growing up, "I didn't have a huge (knowledge) of it," she said. "But it's funny, when we started working on this project, they would always be playing songs and I'd be like, 'Oh, I know all of this.' I just didn't really know the world or who was rapping, but I really learnt. I now have an even bigger appreciation for (the genre)."

Jasper has been an avid rap fan since he was a kid in New Jersey, where the film is set. In many ways, "Patti is my alter ego," he said. "She just popped in my brain one day and was sort of a valentine to the big, strong women that I grew up with. I thought she'd make an amazing, different and subversive kind of rapper in this day and age."

He developed Patti Cake$ in screenwriting and directing labs at the Sundance Institute, and says the script went through 10 wildly different iterations over the years. Coming from a music video background, "you just throw out the craziest ideas," Jasper said. Early versions "took place in a casino and there was a heist and it was so ludicrous. It was an Ocean's Twelve-kind of thing."